RFC 5221 Address-Selection Reqs July 20081. Introduction
Today, the RFC 3484 [RFC3484] mechanism is widely implemented in
major OSs. However, in many sites, the default address-selection
rules are not appropriate, and cause a communication failure. The
problem statement (PS) document [RFC5220] lists problematic cases
that resulted from incorrect address selection.
Though RFC 3484 made the address-selection behavior of a host
configurable, typical users cannot make use of that because of the
complexity of the mechanism and lack of knowledge about their network
topologies. Therefore, an address-selection autoconfiguration
mechanism is necessary, especially for unmanaged hosts of typical
users.
This document contains requirements for address-selection mechanisms
that enable hosts to perform appropriate address selection
automatically.
2. Requirements of Address Selection
Address-selection mechanisms have to fulfill the following eleven
requirements.
2.1. Effectiveness
The mechanism can modify RFC 3484 default address-selection behavior
at nodes. As documented in the PS [RFC5220], the default rules
defined in RFC 3484 do not work properly in some environments.
Therefore, the mechanism has to be able to modify the address-
selection behavior of a host and to solve the problematic cases
described in the PS document.
2.2. Timing
Nodes can perform appropriate address selection when they select
addresses.
If nodes need to have address-selection information to perform
appropriate address selection, then the mechanism has to provide a
function for nodes to obtain the necessary information beforehand.
The mechanism should not degrade usability. The mechanism should not
enforce long address-selection processing time upon users.
Therefore, forcing every consumer user to manipulate the address-
selection policy table is usually not an acceptable solution. So, in
this case, some kind of autoconfiguration mechanism is desirable.
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RFC 5221 Address-Selection Reqs July 20082.3. Dynamic Behavior Update
The address-selection behavior of nodes can be dynamically updated.
When the network structure changes and the address-selection behavior
has to be changed accordingly, a network administrator can modify the
address-selection behavior of nodes.
2.4. Node-Specific Behavior
The mechanism can support node-specific address-selection behavior.
Even when multiple nodes are on the same subnet, the mechanism should
be able to provide a method for the network administrator to make
nodes behave differently. For example, each node may have a
different set of assigned prefixes. In such a case, the appropriate
address-selection behavior may be different.
2.5. Application-Specific Behavior
The mechanism can support application-specific address-selection
behavior or combined use with an application-specific address-
selection mechanism such as address-selection APIs.
2.6. Multiple Interface
The mechanism can support those nodes equipped with multiple
interfaces. The mechanism has to assume that nodes have multiple
interfaces and makes address selection of those nodes work
appropriately.
2.7. Central Control
The address-selection behavior of nodes can be centrally controlled.
A site administrator or a service provider could determine or could
have an effect on the address-selection behavior at their users'
hosts.
2.8. Next-Hop Selection
The mechanism can control next-hop-selection behavior at hosts or
cooperate with other routing mechanisms, such as routing protocols
and RFC 4191 [RFC4191]. If the address-selection mechanism is used
with a routing mechanism, the two mechanisms have to be able to work
synchronously.
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RFC 5221 Address-Selection Reqs July 20082.9. Compatibility with RFC 3493
The mechanism can allow an application that uses the basic socket
interface defined in RFC 3493 [RFC3493] to work correctly. That is,
with the basic socket interface the application can select
appropriate source and destination addresses and can communicate with
the destination host. This requirement does not necessarily mean
that OS protocol stack and socket libraries should not be changed.
2.10. Compatibility and Interoperability with RFC 3484
The mechanism is compatible with RFC 3484. Now that RFC 3484 is
widely implemented, it is preferable that a new address selection
mechanism does not conflict with the address selection mechanisms
defined in RFC 3484.
If the solution mechanism changes or replaces the address-selection
mechanism defined in RFC 3484, interoperability has to be retained.
That is, a host with the new solution mechanism and a host with the
mechanism of RFC 3484 have to be interoperable.
2.11. Security
The mechanism works without any security problems. Possible security
threats are described in the Security Considerations section of this
document.
3. Security Considerations3.1. List of Threats Introduced by New Address-Selection Mechanism
There will be some security incidents when combining the requirements
described in Section 2 into a protocol. In particular, there are 3
types of threats: leakage, hijacking, and denial of service.
1. Leakage: Malicious nodes may tap to collect the network policy
information and leak it to unauthorized parties.
2. Hijacking: Nodes may be hijacked by malicious injection of
illegitimate policy information. RFC 3484 defines both a source
and destination selection algorithm. An attacker able to inject
malicious policy information could redirect packets sent by a
victim node to an intentionally chosen server that would scan the
victim node activities to find vulnerable code. Once vulnerable
code is found, the attacker can take control of the victim node.
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RFC 5221 Address-Selection Reqs July 2008
3. Denial of Service: This is an attack on the ability of nodes to
communicate in the absence of the address-selection policy. An
attacker could launch a flooding attack on the controller to
prevent it from delivering the address selection policy
information to nodes, thus preventing those nodes from
appropriately communicating.
3.2. List of Recommendations in Which Security Mechanism Should Be Applied
The address selection mechanism should be afforded security services
listed below. It is preferable that these security services are
afforded via use of existing protocols (e.g., IPsec).
1. Integrity of the network policy information itself and the
messages exchanged in the protocol. This is a countermeasure
against leakage, hijacking, and denial of service.
2. Authentication and authorization of parties involved in the
protocol. This is a countermeasure against Leakage and
Hijacking.
4. Normative References
[RFC3484] Draves, R., "Default Address Selection for Internet
Protocol version 6 (IPv6)", RFC 3484, February 2003.
[RFC3493] Gilligan, R., Thomson, S., Bound, J., McCann, J., and W.
Stevens, "Basic Socket Interface Extensions for IPv6", RFC3493, February 2003.
[RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and
More-Specific Routes", RFC 4191, November 2005.
[RFC5220] Matsumoto, A., Fujisaki, T., Hiromi, R., and K. Kanayama,
"Problem Statement for Default Address Selection in
Multi-Prefix Environments: Operational Issues of RFC 3484
Default Rules", RFC 5220, July 2008.
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RFC 5221 Address-Selection Reqs July 2008
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